Acoustic navigation and diving information system and method The positions of one or more underwater divers or vehicles are determined through an underwater acoustic communication link and at least a base buoy and one remote buoy with acoustic transponders and GPS position locating equipment. The location of the buoys is determined by the GPS equipment. The underwater diver or vehicle each carries an acoustic tracking unit transponder which emits a tracking unit message specifying its identity and its last known position at an assigned time slot. Upon reception of the tracking unit message by the base buoy, an acoustic base buoy message is emitted which includes the buoy position. The tracking unit receives the base buoy message, and marks the time of arrival to determine the propagation delay between the tracking unit and the base buoy. A predetermined delay after the receipt of the tracking unit message by the remote buoy, it sends an acoustic remote buoy message specifying its location. The tracking unit receives the remote buoy message, marks its time of arrival, and determines its location from the times of arrival and the positions of the buoys. The base buoy can communicate with a base station, passing along all received tracking unit messages so that the base station can keep track of the locations of all tracking units. Commands from the base station can be encoded into the base buoy message, to provide instructions to the various divers and underwater vehicles. Mobile underwater arrays An oceanographic sampling system includes two or more underwater vehicles disposed in an array and an array controller for controlling the array of underwater vehicles as data is acquired. Each underwater vehicle includes a propulsion system for moving the underwater vehicle independently of the other underwater vehicles, a sensor for sensing an ocean parameter and providing sensor data representative of the ocean parameter as the underwater vehicle moves, a navigation subsystem for determining position data representative of the position of the underwater vehicle as the sensor data is acquired and a synchronizing subsystem for time synchronizing the sensor data and the position data acquired by the underwater vehicle with sensor data and position data acquired by other underwater vehicles. The array of underwater vehicles may function as a large aperture phased array, and phased array analysis techniques may be applied to the time-synchronized sensor data and position data. Apparatus and method for deploying, recovering, servicing, and operating an autonomous underwater vehicle An apparatus and methods for deploying, recovering, and servicing an AUV are disclosed. The apparatus includes a linelatch system that is made up of a tether management system connected to a flying latch vehicle by a tether. The linelatch system can be connected to a surface vessel by an umbilical on one end and to an AUV on the other end. In addition to providing a mechanical connection, between the AUV and a surface vessel, the linelatch system can also carry power and data between the surface vessel (i.e., through the umbilical) and the AUV. Underwater object positioning system An underwater object positioning system comprises a workboat, an acoustic transmitter-receiver mounted on the workboat, first and second surface tow units towed by the workboat, an acoustic transducer that is mounted on the first surface tow unit, that is connected by a communication cable to the acoustic transmitter-receiver on the workboat and that is positioned by a radio positioning means; two acoustic receivers that are mounted on the second surface tow unit, that are connected by a communication cable to the acoustic transmitter-receiver on the workboat and that are positioned by a radio positioning means. An acoustic pulse transmitter is mounted on a submerged positioning target. A processor unit on the workboat calculates the location of the submerged target based on data showing the positions of the transducer and receivers, and the distances from the transducer and receivers to the acoustic pulse transmitter. Baffled ring directional transducers and arrays The present invention relates to a directional electro-acoustic transducer and arrays of transducers of the cylindrical or ring electro-mechanical type in conjunction with a partial conformal acoustic baffle. Such a device has very desirable directional beam patterns that are nearly frequency independent over a significant frequency range and the radiation is has a characteristic broadband frequency response due to multimode excitation. Subsea navigation and survey A subsea navigation system comprising a plurality of spaced antenna means provided on a subsea structure arranged to emit electromagnetic radiation. A detection means is provided on a subsea vehicle for receiving and analyzing the electromagnetic radiation transmitted by the antenna means allowing the subsea vehicle to navigate relative to the subsea structure. Each of the antenna means comprises a cathodic protection anode provided on the subsea structure.